Surgical depth instrument

ABSTRACT

An instrument that measures the depth of an open or closed hole in a bone or other tissue electronically, provides a rotatable display of information relating to the depth. The surgical depth gauge comprises a probe insertable into the hole that measures a depth that is communicated to the rotatable display. The display may be rotatable in one, two, or three dimensions, and may be implemented as a wired or wireless display. A locking mechanism may be provided to lock the display in a particular orientation best suited for a particular situation.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of co-pending U.S. patent applicationSer. No. 12/391,814, filed Feb. 24, 2009, which is acontinuation-in-part of U.S. patent application Ser. No. 11/376,399,filed Mar. 15, 2006, now issued as U.S. Pat. No. 7,493,703, which is acontinuation-in-part of U.S. patent application Ser. No. 11/081,147,filed on Mar. 16, 2005, now issued as U.S. Pat. No. 7,165,336, theentire content of these being herein incorporated by reference.

BACKGROUND

The invention relates to an instrument for determining the depth of anopen or closed hole and, in particular, a depth gauge for providing adigital measurement of the depth of the open or closed hole in a bone.

Many surgical procedures require surgeons to secure a device to the boneof a patient. In some procedures, the surgeon spans and secures one ormore bones, or pieces of bone, using a bone plate and screws or otherfasteners. In other procedures, the surgeon uses a screw or otherfastener without another device, for example, to secure a transplantedtendon. In many procedures, the surgeon drills a hole in the bone priorto securing the fastener to the bone. With a hole in place, the surgeoncan more easily select a fastener of the appropriate length. Selecting afastener of appropriate length can be very important. If the fastener istoo long, the fastener may protrude from the bone. Typically, the boneabuts against soft tissues that may be harmed if the fastener is toolong. Although over-drilling through a metacarpal may result only inminor damage to the fat layer within the finger, if the fastener usedafter drilling is too long, the patient may experience more seriouscomplications. For example, a fastener that protrudes may be tactilelyfelt by the patient, prevent soft tissues (such as tendons, ligaments,or muscles) from moving over the bone surface, or even pierce the skin.As a different example, complications such as paralysis may result froma fastener mounted in the pedicle portion of the human spine thatprotrudes to a point where the fastener contacts the spinal cord.

During drilling, the surgeon is typically capable of feeling when thedrill has penetrated through the bone from a drop in resistance of thedrill against the bone. Because the simple act of drilling does notprovide an exact measurement of the depth of the bone, surgeonssometimes use an analog depth gauge to measure the depth of the hole.

Analog depth gauges typically comprise a central probe member having abarb at the distal end, and a reciprocating sleeve that encircles theproximal end of the central probe member. To measure the depth of a holein a bone, the surgeon abuts the sleeve against the proximal side of thehole, and extends the probe member into the hole. After extending theprobe member beyond the distal side of the hole, the surgeon retractsthe probe member, attempting to find purchase against the distal side ofthe hole with the barb. Typically, a marker is secured to the centralprobe member and the reciprocating sleeve has a graduated scale (ininches or millimeters) along a portion of its length. The surgeon readsthe measurement of depth by examining the position along the graduatedscale indicated by the marker secured to the central probe member.

A number of problems are associated with the analog depth gauge.Components of the analog depth gauge are typically manufactured fromsurgical-grade stainless steel, with the graduated scale embossed alonga portion of the length of the reciprocating member, producing a highlyreflective surface. Under bright operating room lights, surgeons find itdifficult to see the graduated scale of millimeter-wide lengthincrements. An accurate measurement of depth using an analog depth gaugerequires the surgeon to make a close examination of the graduated scalewhile holding the analog depth gauge steady. If the barb loses itspurchase on the distal side of the hole, either the accuracy of themeasurement is decreased or the time required for surgery must beextended to permit repositioning of the barb. In surgical proceduresthat require many depth measurements, these difficulties are multiplied.

There are other problems associated with the analog depth gauge. Anaccurate reading of the graduated scale requires the eyes of the surgeonto be properly aligned with the graduated scale. Viewed from an angle,the position of the marker relative to the graduated scale may bedistorted. The eyes of the surgeon may not be properly aligned with thegraduated scale while the surgeon is standing erect. The surgeon mayhave to bend over while using the analog depth gauge to make an accuratereading because if the depth gauge is tilted in order to make thereading, the sleeve will shift relative to the probe, making themeasurement less accurate and possibly causing the barb to lose itspurchase on the distal side of the hole, resulting in the samedisadvantages mentioned above.

Accordingly, there has been a need for an improved depth gauge forsurgical procedures.

SUMMARY

The present invention provides a system for faster and more accuratemeasurements of depth during surgery and permits an adjustment of theorientation screen to permit easy viewing of a display that providesdepth measurement information.

Accordingly, in an embodiment of the invention, a generally elongatedinstrument is provided for measuring the depth of a hole with a firstedge and a second edge, the instrument having a longitudinal axis, theinstrument comprising: a first generally elongated member substantiallyoriented along the longitudinal axis and which is insertable in thehole, the first member comprising a portion positionable against a firstsurface in which the first edge of the hole is formed; a secondgenerally elongated member substantially oriented along the longitudinalaxis and which is slidably connected to the first member, the secondmember comprising a portion positionable against a second surface inwhich the second edge of the hole is formed and a sensor that generatesan electronic signal that varies in relation to the distance between thefirst member and the second member; and a rotatable electronic displayfor displaying information representative of the distance measured bythe sensor.

In another embodiment, a depth measurement gage is provided formeasuring a hole depth, comprising: a measurement tool that converts anextension length of a measuring element into a representative electronicsignal; a display assembly connected to the depth measurement gage, thedisplay assembly comprising: a rotatable display that comprises: adisplay screen for displaying a numeric representation corresponding tothe extension length based on the electronic signal received from themeasuring tool; display electronics that receive the electronic signal,converts it into a displayable value, and drives the display to displaythe value; and a locking mechanism that holds the display at aparticular orientation; wherein the rotatable display is rotatable aboutan axis normal to a surface of the display screen; the display assemblyfurther comprising: a housing that connects with and supports therotatable display; the depth measurement gage further comprising: arotation element that allows the rotatable display to rotate about anaxis parallel to a surface of the display screen.

In another embodiment, a depth measurement gage is provided formeasuring a hole depth, comprising: a measurement tool that converts anextension length of a measuring element into a representative electronicsignal; an elongated housing extending along a longitudinal axis of themeasurement tool; a rotatable rectangular display that, when in aninitial position, has a side that is parallel to the longitudinal axis,the display comprising: a display screen for displaying a numericrepresentation corresponding to the extension length based on theelectronic signal received from the measuring tool; display electronicsthat receive the electronic signal, converts it into a displayablevalue, and drives the display to display the value; and a lockingmechanism that holds the display at a particular orientation; whereinthe rotatable display is rotatable about an axis normal to a surface ofthe display screen.

In another embodiment, a depth measurement gage is provided formeasuring a depth of a hole, comprising: a measurement tool thatconverts an extension length of a measuring element into arepresentative electronic signal that is wirelessly transmitted; adisplay assembly connected to the depth measurement gage, the displayassembly comprising: a wireless rotatable display that comprises: adisplay screen for displaying a numeric representation corresponding tothe extension length based on the electronic signal received from themeasuring tool; a wireless antenna and signal receiver that receives thewirelessly transmitted electronic signal; and display electronics thatreceive the electronic signal, converts it into a displayable value, anddrives the display to display the value; the display assembly furthercomprising: a housing that connects with and supports the rotatabledisplay.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, advantages, and features of the presentinvention will be apparent from the following detailed description andthe accompanying drawings illustrating various embodiments of theinvention, in which:

FIG. 1 is a perspective view from above of a surgical depth instrumentin accordance with an embodiment of the present invention;

FIG. 2A is a cross-section of a surgical depth instrument in a retractedposition in accordance with an embodiment of the present invention;

FIG. 2A′ is an enlarged pictorial detail view of a circled portion ofthe cross-section shown in FIG. 2A;

FIG. 2B is a cross-section of a surgical depth instrument in an extendedposition and engaged with the distal surface of a bone portion inaccordance with an embodiment of the present invention;

FIG. 2B′ is an enlarged pictorial detail view of a circled portion ofthe cross-section shown in FIG. 2B;

FIG. 3 is an exploded perspective view of a sealed housing in accordancewith an embodiment of the surgical depth instrument of the presentinvention;

FIG. 4 is a perspective view from below of a surgical depth instrumentin accordance with an embodiment of the present invention;

FIG. 5 is a cross-section view of the sealed housing and body of asurgical depth instrument in accordance with an embodiment of thepresent invention, taken at section line 5-5 of FIG. 4;

FIG. 6A is a pictorial view of a probe with a barb in accordance with anembodiment of the present invention;

FIG. 6B is a pictorial view of a probe with a hook in accordance with anembodiment of the present invention;

FIG. 7 shows a surgical depth instrument in accordance with a secondembodiment of the present invention;

FIG. 8 is an exploded perspective view of an exemplary display assemblyaccording to an embodiment of the invention;

FIG. 9 is an assembled perspective view of the display assemblyillustrated in FIG. 8;

FIG. 10 is a perspective bottom view of a lower display housing;

FIG. 11 is a perspective view of an exemplary transparent cover of thedisplay assembly;

FIG. 12 is a perspective view of a locking slider of the displayassembly;

FIG. 13 is a perspective view of the display assembly pivotally mountedto a pivot arm;

FIG. 14 is a perspective view of a display assembly according to anotherembodiment of the invention;

FIGS. 15A, 15B are top views of further embodiments of the invention;

FIG. 15C is a top view of the embodiment shown in FIGS. 15A and 15Bshowing a rotated display; and

FIG. 15D is a top view of the embodiment shown in FIGS. 15A-15Cillustrating a rotation about the longitudinal axis of a sectioncomprising the display.

DETAILED DESCRIPTION OF THE EMBODIMENTS

After drilling a hole in a bone during surgery, a surgeon will often usean instrument to measure the depth of the hole before selecting afastener. The system and method of the present invention are performedusing a surgical depth gauge with an electronic sensor and digitaldisplay, which provide an easier, faster, and more accurate means formeasuring depth during surgery. While a variety of embodiments of theinvention are shown in the attached figures, those skilled in the artwill recognize that there are other mechanical and electricalarrangements for accomplishing surgical depth measurements digitally inaccordance with the present invention. Various alternative embodiments,features and variations are therefore also described herein.

Instruments used for surgical procedures must be robust both to thesolid and liquid contaminants encountered during surgery (such as tissueand blood) and the temperatures, pressures, and fluids encounteredduring sterilization (such as hydrogen peroxide gas). The twoembodiments of the present invention shown in the attached drawingsillustrate two alternative form factors for the sterilization-proof andcontamination-proof surgical depth gauge in accordance with the presentinvention. In a first embodiment 100 shown in FIGS. 1 through 5, thesurgical depth gauge comprises a tissue guard 120, sealed housing 130,and body 140 that are robust to contamination. In addition, the firstembodiment 100 can be quickly disassembled and reassembled forsterilization. In a second embodiment 200 shown in FIG. 7, the surgicaldepth gauge comprises a fully integrated body 235, in which is sealed anelectronic sensor and displays. The second embodiment is robust torepeated contamination and sterilization without disassembly.

With a hole already drilled, a surgeon might reach for a surgical depthinstrument of the present invention as shown by the instrument 100 ofFIG. 1. The instrument 100 comprises a probe 160 with an indented hook165, and a tissue guard 120 secured to a body 140. A sealed housing 130slidably engages with a side groove 144 of the body 140 of theinstrument 100. As shown in FIG. 1, the sealed housing 130 comprises adisplay window 150, ergonomic top ridges 170, and ergonomic side grooveswith ridges 180. The present invention is adapted for use by either aleft-handed or a right-handed surgeon. The side grooves with ridges 180are concave to the side surface of the sealed housing 130, and aresymmetrically disposed on either side of the sealed housing 130.

An alternative embodiment of the form factor for the present inventionis shown in FIG. 7 as the second embodiment 200. In this alternativeembodiment, the invention comprises a substantially cylindrical formfactor. As discussed above, the second embodiment 200 comprises anintegrated body 235 that is robust to contamination and sterilizationwithout disassembly. Referring to FIG. 7, the second embodiment 200comprises an integrated body 235 with slide groove 239 and displaywindow 250 formed therein. In accordance with an embodiment, so that thesame instrument may be used by both right-handed and left-handedsurgeons, a display window 250 (and accompanying display) will beprovided on both the right and left sides of the instrument. In otherwords, with respect to FIG. 7, another display window 250 (and display)will be similarly disposed on the other side of the instrument. Thedistal end of the integrated body 235 includes a tissue guard 220. In anembodiment, the method of the present invention is practiced bypositioning the distal end of the tissue guard 220 against the proximalsurface of the bone (as shown in connection with FIGS. 2A and 2B,described below). According to an embodiment, the integrated body 235 ofthe instrument 200 may be fabricated from two substantially symmetricalpieces that may be disassembled and reassembled to facilitatesterilization. As shown in FIG. 7, the two pieces fit together along aline through the middle of the integrated body 235. In variousembodiments, the two pieces may be threaded together, or sealed togetherby an adhesive resistant to contamination and sterilization. Inaddition, as shown in FIG. 7, the second embodiment form factor 200 alsocomprises finger grooves disposed towards its bottom side.

Turning back to the first embodiment of the form factor shown byinstrument 100 in FIG. 1, the instrument 100 includes side grooves 180,which are formed in the bottom piece 139 of the sealed housing 130 (seeFIG. 3). In other embodiments, however, the side grooves 180 may beformed in both the top piece 138 and bottom piece 139, such that theside grooves extend from top to bottom symmetrically along the sides ofthe sealed housing 130. As will be appreciated by those of skill in theart, in still other embodiments, the side grooves 180 may be convex tothe side surface of the sealed housing 130, and may be formed with asurface of bumps rather than ridges, or with other surfaces that providefriction and a tactile surface, even after exposure to solid or liquidcontamination. In addition, in all of the embodiments shown in theattached drawings, the display window 150 is positioned nearer thedistal end of the instrument. As will be appreciated by those of skillin the art, the display window 150 may be positioned elsewhere on theinstrument, for example, nearer the proximal end. In addition, multipledisplay windows may be disposed at various locations on the instrument.All such features and variations are contemplated within the scope ofthe present invention.

An embodiment of the method for taking depth measurements in accordancewith the present invention begins with the surgeon holding theinstrument 100 in either a right or a left hand. FIG. 2A shows alongitudinal cross-section of the instrument 100 with the probe 160 in aretracted position, and a bone portion 10 shown also in cross-section.In accordance with an embodiment of the method of the present invention,the surgeon begins a depth measurement by locating the position of thehole in the bone portion 10. As shown in the enlarged detail of FIG.2A′, the tip of the indented hook 165 protrudes slightly beyond thedistal end 122 of the tissue guard 120, thereby permitting the surgeonto sense the position of the hole when the tip of the indented hook 165slips into the hole. In this position, the distal end 122 of the tissueguard 120 abuts against the proximal surface 30 of the bone portion 10.In an embodiment, the instrument 100 is calibrated to read zero depthwhen the catch (or the proximal end) of the hook 165 is flush with thedistal end 122 of the tissue guard 120.

In an embodiment, the method of the present invention also comprises astep wherein the surgeon extends the probe 160 into the hole 20 of thebone portion 10. FIG. 2B shows a cross-section of the instrument 100 inan extended position. FIG. 2B′ shows an enlarged detail of FIG. 2B, inwhich the indented hook 165 has purchase on the distal surface 40 of thehole 20. In the cross-sections shown in FIGS. 2B and 2B′, the distal end122 of the tissue guard 120 remains against the proximal surface 30 ofthe bone portion 10 in which a hole 20 is present. From the positionshown in FIG. 2B′, the surgeon reads a measurement of depth from anelectronic display behind the display window 150 in the compartment 134of the sealed housing 130.

As shown in FIGS. 2A′ and 2B′, the bone portion 10 is bicortical, i.e.,the bone portion 10 has a first, proximal cortical layer 12 (see FIG.2A′), a cancellous layer 14, and a second, distal cortical layer 16 (seeFIG. 2B′). It should be noted, however, that the present invention issuitable for use with bones having other structures, including solidcortical, unicortical, or cancellous bones. The present invention mayeven be used for surgical depth measurement of holes or cavities inother types of tissue.

As described above, the hole 20 may be a hole formed in the bone portion10. In using the instrument 100 to measure the distance from a proximalsurface 30 formed on the proximal cortical layer 12 to a distal surface40 formed on the distal cortical layer 16, the instrument 100 operatesso that the distance between the distal end 122 of the tissue guard 120(which abuts the proximal surface 12) and the proximal end of theindented hook 165 (which has purchase on the distal surface 16) isdetermined by an electronic sensor, generating a precise measurement ofthe distance between the proximal surface 30 and distal surface 40. Theelectronic sensor may comprise inductive or capacitive elements in aread assembly on a printed circuit board and inductive or capacitiveelements in an increment assembly on a printed circuit board within thecompartment 146 of the body 140 (see FIG. 5). More specifically, theprobe 160 of the instrument 100 is inserted into the proximal edge 22 ofthe hole 20, through the hole 20, and out from a distal edge 26 of thehole 20, such that the indented hook 165 of the probe 160 extends beyondthe distal surface 40 of the bone portion 10. Extension of the indentedhook 165 away from the body 140 is accomplished in accordance with theinstrument 100 by pressing a thumb or forefinger against the top ridges170 on the sealed housing 130. As should be clear to those of ordinaryskill in the art, if the hole 20 is a hole formed by a drill bit ofcylindrical symmetry, the proximal and distal edges 22 and 26 will beapproximately circular.

The distal end of the probe 160 is equipped with an indented hook 165 inthe instrument 100 shown in FIGS. 1, 2, 4 and 7. In other embodiments,however, the indented hook 165 may be replaced with another means fordetecting the distal surface 40. In particular, FIGS. 6A and 6B show inprofile alternative mechanical embodiments of the distal end of theprobe 160. FIG. 6A shows a barb 167 at the distal end of the probe 160.FIG. 6B shows a hook 169 at the distal end of the probe 160.

With the indented hook 165 at its distal end, the probe 160 can takepurchase on the distal surface 40 of the bone portion 10. The instrument100 is shown in this position in FIGS. 2B and 2B′. Once the indentedhook 165 has completely passed through the distal edge 26, the shaft ofthe probe 160 is shifted slightly, laterally so that the indentation inthe indented hook 165 abuts against the distal edge 26. A slightretraction of the probe 160 then permits the indented hook 165 to engage(or take purchase on) the distal surface 40 of the distal cortical layer16. Retraction of the indented hook 165 is accomplished in accordancewith the instrument 100 by squeezing the side grooves 180 with thumb andforefinger, and pulling lightly. In this manner, the proximal surface ofthe indented hook 165 and the distal end of the tissue guard 120,respectively, are positioned against the distal surface 40 and proximalsurface 30 of the bone portion 10 and, through the use of slighttension, are retained thereon. In reading the electronic display whenthe invention is maintained in this physical configuration, the surgeonis provided with an accurate measurement of the depth of the hole 20 inthe bone portion 10.

Although in the embodiment depicted in FIG. 1, the probe 160 includes amechanical securement (in the form of an indented hook 165), othermechanical and nonmechanical means for positioning the distal end of theprobe 160 against the distal surface 40 of the bone portion 10 may beused in other embodiments of the present invention. In particular,electronic sensors may be used in other embodiments to detect where thedistal surface 40 terminates. For example, an ultrasonic transducer,optical or other sensor may be used to detect where the distal surface40 terminates by measuring differential acoustic or optical reflectivityor transmissivity or other characteristics as the probe 160 traversesthe hole 20. In such embodiments, an electronic sensor may be mounted tothe distal end of the probe 160 in a configuration perpendicular to thelength of the probe 160. Alternatively, the distal end of the probe 160may include only a perforation disposed perpendicular to the length ofthe probe 160, and a conduit that provides an acoustical, optical, orelectrical connection to a sensor included in the sealed housing 130. Aswill be recognized by skilled artisans, such a conduit might be providedby a hollow probe, fiber optic, or insulated wire, respectively.Moreover, in some embodiments, a current-sensing device may be placed inelectrical connection (for example, with an insulated wire) with thedistal end of the sensor to detect a change in the resistivity orconductivity of the environment local to the distal end of the probe160.

The instrument 100 further includes a reference portion that abuts theproximal surface 30. In the embodiment of the invention shown in theattached drawings, the reference portion is provided by a tissue guard120. The tissue guard 120, as shown by way of example in FIGS. 1, 2, 4and 7, has a tapered conical shape. The tissue guard includes acylindrical hollow at its core, through which the probe 160 may extendand retract. In other embodiments, the tissue guard may take a narrower,longer, or more elongated shape to permit easier passage through tissuesdisposed between the surgeon and the proximal surface 30 of the boneportion 10. For example, in another embodiment, the tissue guard 120 maybe replaced with a simple cylindrical sleeve fitted into a conical pieceat the distal end of the body of the instrument. The tapered conicalshape of the tissue guard 120 shown in FIGS. 1, 2, 4 and 7, however, maybe desirable for minimizing mechanical stress at the joints between thetissue guard 120 and body 140.

In an embodiment, the end of the body 140 nearest the tissue guard 120has a threaded nipple (not shown in FIG. 1) of diameter larger than thediameter of the probe 160. In the instrument 100, the threaded nipple isintegrally formed with the end of the body 140. In another embodiment,the threaded nipple may be secured to the distal end of the body 140 bya mechanical device or an adhesive. In all such embodiments, the tissueguard 120 is provided with a complementary threaded surface such thatthe tissue guard 120 and body 140 are secured by threading the tissueguard 120 onto the threaded nipple of the body 140. In such embodiments,the tissue guard 120 may be formed from injection molded plastic or frommachined metal. In other embodiments, the tissue guard 120 may be formedas a single, seamless piece with the body 140.

The tissue guard 120 and probe 160 are concentrically arranged such thatthe distal end of the tissue guard 122 abuts the proximal surface 30 ofthe bone portion 10 in a manner similar to that of a bone plate orfastener head. Accordingly, the tissue guard 120 and indented hook 165cooperate such that their relative position (and, therefore, distance)provides an accurate measurement of the depth of the hole 20 such that ascrew or fastener may be selected whose length is accommodated by thehole 20.

In the embodiment of the invention provided by the instrument 100,movement of the sealed housing 130 is effective to shift the position ofthe probe 160 because the probe 160 and sealed housing 130 are attachedas shown in FIG. 3. A portion of the bottom side of the sealed housing130 is formed into a mating surface 132. The probe 160 is encircled byand secured within the portion of the bottom side of the sealed housingthat forms the mating surface 132. In an embodiment, the probe 160 isinterference press-fit into the bottom piece 139 of the sealed housing130. Also shown in FIG. 3 are the mechanical parts of the sealed housing130, including the top piece 138, bottom piece 139, and seal 136. In anembodiment, the seal 136 is an o-ring seal, which is robust to repeatedcontamination and sterilization. In addition, FIG. 3 shows the displaywindow 150, which in an embodiment of the invention, is provided by apolycarbonate lens. The compartment 134 within the sealed housing 130provides the mechanical support for the electronic sensor and display(not shown in FIG. 3). As described below, the electronics secured tothe compartment 134 within the sealed housing 130 comprise the read-headassembly of an inductive or capacitive or other sensor, a display, and apower source (such as a battery).

In the embodiment of the sealed housing 130 shown in FIG. 3, electroniccomponents (including an electronic sensor, display, and power source)are sealed inside the compartment 134 with an o-ring seal 136. Inaddition, the sealed housing 130 may be sealed with epoxy, glue, orother adhesives. In other embodiments, the sealed housing 130 may bemechanically sealed with hardware, such as screws or snaps within thecompartment 134. Although the embodiment of the sealed housing 130 shownin FIG. 3 is designed to remain sealed both during surgery andsterilization, it will be appreciated by those skilled in the art thatin an alternative embodiment, the sealed housing 130 may be designed topartially or completely disassemble for sterilization. All thesefeatures and variations are contemplated within the scope of the presentinvention.

When sealed, the embodiment of the sealed housing 130 shown in FIG. 3 iswater resistant to several atmospheres of pressure. Moreover, thematerials used to manufacture the sealed housing 130 are selected to bechemically inert to chemical contaminants or sterilization fluids, bothat room temperature and at the temperatures required for sterilizationin an autoclave. For example, the sealed housing 130 may be molded fromacrylic, polyester, PVC, or other chemically inert plastic material. Inother embodiments, the sealed housing may be made from metals, such asaluminum, brass, or stainless steel. The sealed housing 130 is alsodesigned to provide only soft, rounded edges that are safe for use in asurgical environment. For example, the embodiment of the sealed housing130 shown in FIGS. 1 through 5 is in substantial compliance with theUnderwriters Laboratories sharpness test UL 1349.

Although the instrument 100 shown in the attached drawings includes adisplay, it will be understood by those of skill in the electronic artsthat the present invention may be practiced using an external display incommunication with a wireless device. In the instrument 100, a wirelesstransmitter may be connected to the read-head assembly within the sealedhousing 130. In such wireless embodiments, a wireless receiver would bepositioned a short distance away from the surgical depth gauge (forexample, on a platform near the operating table), and an electronicdisplay would be connected to the wireless receiver. In addition, as asupplement to a visual display, the instrument may be provided with anaudio readout capability that may, for example, beep or provide anotheraudible signal when the instrument senses that movement of the probe hasstopped, and there has been an appropriate interval in which to take ameasurement. In addition, the instrument may include the capability forthe distance displayed to also be audibly conveyed through a simulatedvoice from a speaker maintained within the instrument. In this manner,the surgeon's determination of the distance may also be verified fromthe audible articulation of the distance, providing further confidencein the accuracy of the reading.

A perspective view of the instrument 100 from the bottom is shown inFIG. 4. As shown in FIG. 4, the present invention includes severalergonomic features in addition to the top ridges 170 (shown in FIGS. 1and 3). In particular, the instrument 100 includes symmetrically shapedside grooves with ridges 180 and finger grooves 190. As shown in thecross-sectional end view of FIG. 5, the finger grooves 190 are formed inthe convex bottom side 192 of the body 140. In accordance with anembodiment of the method of the present invention, a surgeon would placea forefinger on a first side groove 180, a thumb on the opposing sidegroove 180, and the rest of the fingers on the finger grooves 190integrated with the body 140. The ergonomic design of the presentinvention permits a surgeon to use the system and perform the method ofthe present invention with a single hand, either right or left.Moreover, the present invention leaves the bottom side 192 entirelyunobstructed so that the surgeon is always free to grab the body 140.

Some structural features of the invention shown in FIG. 5 have theadvantage of permitting the instrument 100 to be disassembled andreassembled for sterilization. In particular, the sealed housing 130 andbody 140 are slidably connected along a mating surface 132 of the sealedhousing 130 and a reciprocal mating surface 142 formed within the sidegroove 144 of the body 140. The probe 160, which is engaged in thesealed housing 130, slides through the side grooves 144 of the body 140and into a funneled cylindrical channel formed in the tissue guard 120.In another embodiment, the tissue guard 120 may provide a keyhole-shaped(rather than a cylindrical) channel to permit probe tips withoutcylindrical symmetry (i.e., tips such as the barb 167 or hook 169 shownin FIGS. 6A and 6B) to pass through during disassembly and reassembly ofthe instrument 100. Moreover, in such other embodiments, the tissueguard 120 may be rotated after assembly to prevent the distal end of theprobe 160 from retracting within the tissue guard 120. Such a rotationis permitted when the tissue guard 120 threads onto the body 140, asdescribed above. Without a keyhole-shaped channel, probe tips ofnon-cylindrical symmetry must have a maximum width less than the totaldiameter of the cylindrical channel in the tissue guard 120.

When slidably connected as shown in the instrument 100, the presentinvention does not require oil lubricants, such that the materials areentirely compatible with a surgical environment. Referring to FIG. 3,the instrument 100 is shown in cross-section (along the plane 4-4through the sealed housing 130 shown in FIG. 3) viewed facing the distalend. The sealed housing 130 is shown in FIG. 3, with the compartment 134(again, shown without internal electronic components), and top ridges170. The seal 136 is also shown disposed between the top piece 138 andbottom piece 139 of the sealed housing 130. In addition, the matingsurface 132 of the bottom piece 139 is shown engaged with the reciprocalmating surface 142 formed by and within the side groove 144 of the body140. Also, the probe 160 is shown concentric to the end of the matingsurface 132 of the bottom piece 139. By permitting a slidable connectionbetween the sealed housing 130 and body 140, the mating surface 132 ofthe housing 130 and complementary mating surface of the body facilitatedisassembly and reassembly of the instrument 100 for sterilization.Moreover, because the surfaces are not symmetric from left to rightalong the line 5-5 in FIG. 5, the system can be reassembled only withthe display facing the distal end. The non-symmetrical design of thecomplementary mating surfaces thus prevents the present invention frombeing reassembled incorrectly.

The electronic sensors used in the system and method of the presentinvention comprise capacitive and inductive sensors and sensorassemblies. Sensors and sensor assemblies are readily availablecommercially from manufacturers such as Sylvac and Mitutoyo. Forexample, capacitive and inductive read-head and write-head assembliesare used in digital calipers, such as that made by Mitutoyo AmericaCorporation, 965 Corporate Blvd., Aurora, Ill., and by Guilin Measuringand Cutting Works, 106 Chongxin Road, Guangxi, Guilin 541002, PeoplesRepublic of China. In general, the electronic sensor secured within thecompartment 134 of the sealed housing 130 takes the form of aconventional electronic sensor, display, and power source assembly foruse in a length measuring device relying on inductive or capacitive orother elements. For some embodiments, inductive elements may provideadvantages to the extent that inductors provide more uniform andconsistent measurements through a wider variety of environmentalconditions. For example, the instrument 100 may be built with a patternof inductive loops laid down along the sensor pattern compartment 146 ofthe body 140, and a facing read-head assembly secured within thecompartment 134 of the sealed housing 130.

In various embodiments of the present invention, the electronic sensormay be connected with a microprocessor or other digital electronicdevice in order to produce an output for an electronic display, such asa liquid crystal display or light-emitting diode display. In otherembodiments, the microprocessor or other digital electronic device maybe connected to a wireless transmitter, as described above. In someembodiments, a signal conditioning circuit may interpose the inductiveor capacitive elements of the electronic sensor and the microprocessoror other digital electronic device used to drive the display, thusensuring that correct input current and voltage levels are provided tothe various components. As will be recognized by skilled artisans, apower source, such as a primary or secondary battery, may be connectedto the signal conditioning circuit or to the microprocessor directly.

The microprocessor or other digital electronic device used to drive thedisplay may be configured to provide depth measurements in inches,millimeters, or fractions thereof. In various embodiments, the sealedhousing 130 may include buttons that permit the surgeon to select howthe preferred unit of measurement is displayed. In an embodiment, themicroprocessor or other digital electronic device is configured toprovide a positive reading for depth as the probe 160 is extended fromthe proximal surface 30 toward the distal surface 40 of the bone portion10, and a zero reading when the probe 160 is retracted so that the catchof the hook is flush with the distal end of the tissue guard. In anotherembodiment, the present invention may be configured to permit are-zeroing of the device by providing a calibration button. In stillother embodiments, the present invention may provide on and off buttons(or an on/off toggling button), or a button for storing and holding themeasurement presently shown on the display for reading after the probe160 has been moved. In such embodiments, the buttons may be formed inthe sealed housing 130.

The electronic display of the present invention is selected for quickand easy visual inspection during surgery. The electronic display,however, may provide information in addition to depth measurements. Forinstance, the present invention may be provided as part of a kit (notshown) including a bone plate that mates with a head and shank formed ona screw. The electronic sensor may be calibrated to compensate for orprovide an offset corresponding to a portion of the screw head and shankreceived within the bone plate. Accordingly, the present invention couldbe configured to suggest a particular screw selected from the kit foruse with the bone plate, rather than a measurement of length. Theelectronic display may also provide an indication that the reading isnot stable, for example, because the tissue guard 120 and probe 160 arenot generally stationary relative to one another. This event is moretypical when compressible soft tissue is caught on the indented hook165, or between the tissue guard 120 and the proximal surface 30, or ingeneral when the distal end of the probe 160 is not securely positioned.In this respect, it should be noted that the probe 160 may be providedwithout any mechanical securement at its distal end. As an example, thedistal end of the probe 160 may be inserted to a depth such that itsdistal end is coincident with, but generally does not extend beyond, thedistal edge 26 of the hole 20. In using such an embodiment, the surgeonmay place a stop or finger on the distal surface 40 of the bone portion10 to stop the probe 160 when it has reached the distal edge 26.

In an embodiment, the electronic sensor and accompanying electronics canbe shielded from electromagnetic interference, for example, by coatingthe inside of the sealed housing 130 with a conductive paint containingmetal microspheres. Such shielding may be effective in reducinginterference from low frequency magnetic fields, or other strayelectromagnetic fields. Shielding is desirable at least because themethod of the present invention may be practiced in conjunction with theuse of a magnetic pad for holding surgical instruments (not shown inFIGS. 1-3).

Although the displays shown in FIGS. 1-7 can generally be seen by a userof the device, clearly a display that can be oriented in differentdirections advantageously assist the viewability of the display,particularly under the conditions in which the device would be used.

Therefore, referring to FIGS. 8 and 9, a rotatable display assembly 300is provided that permits better viewability depending on the orientationof the measuring device. This rotatable display assembly 300 shown inFIG. 9 may be mounted directly to an end of the probe 100, 200, or maybe mounted via a pivot arm 391, as is illustrated in FIG. 13.

Referring to FIG. 8, the display assembly, according to an embodiment ofthe invention, is made up of three primary components that can be brokendown in more detail: an upper housing 310, a rotatable display 340, anda lower housing 370. The upper 310 and lower 370 housing provide astructure in which the rotatable display 340 may be mounted and lockedat a particular orientation.

The display 340 is preferably a generally circular shape and comprises adisplay screen 350 along with display electronics 352 that are used tooperate the display screen 350. The display screen 350 is preferably aliquid crystal display (LCD), since this is a relatively low-power typeof display well suited for a measuring instrument. This LCD displaycould provide some form of back-lighting that is known in the art. Thedisplay screen 350 could also be implemented as a light-emitting diode(LED) display. This display, while consuming greater power than the LCDdisplay, could serve to improve readability. Also, other displaytechnologies, such as organic light-emitting diodes (OLED) and the likecould be utilized. The display could be arranged in a number of ways,ranging from a simple seven-segment numeric display to a screen displaycomprising a color pixel grid. The display screen 350 and displayelectronics 352 are affixed within a circular housing comprising anupper 342 and a lower 360 housing component.

In order to permit a locking and holding of the display 340 at aparticular orientation, one or both of the following may be provided: aplurality of locking holes 346 on a side edge of the upper displayhousing 342, and a plurality of locking grooves 348 also located on aside edge of the upper 342 and lower 360 housing components. It shouldbe noted that the location of the locking holes 346 and/or lockinggrooves 348 could be provided on the lower housing 360, or even on anupper or lower surface of the housing components 342, 360. The operativeaction of the locking holes 346 and locking grooves 348 will bedescribed in more detail below along with the other elements with whichthey interact.

The upper housing component 342 may provide a window 344 through whichthe display screen 350 can be read. It is also possible that the upperhousing component 342 would have a clear surface through which thedisplay screen 350 could also be read.

Referring to FIGS. 8 and 10, the lower display housing 360 comprises apin 364 about which the display 340 rotates. Additionally, when thedisplay 340 is a wired display, the lower display housing may comprisewire slots 362 via which wires can be provided to the display screen 350and electronics 352. The wires could be provided via connectors or couldbe soldered directly to circuitry of the display. Other channels can beprovided for getting the wires to the wire slots 362. Stops, such asinterfering protrusions provided on the display 340 and an adjacent partof the display assembly 300 could be provided that prevent rotationbeyond a certain limit.

When the display 340 is a wireless display, then no such access slots362 need to be provided. Such a display 340 may be easily placed intothe display assembly 300 and become operative with little effort. Forthe wireless display 340, the display electronics 352 comprises anantenna and receiver that can read signals provided by the measuringdevice itself. Any form of short range wireless communication hardwareand protocol may be utilized here.

In the embodiment shown in FIGS. 8 and 9, the display 340 is providedbetween the upper housing 310 and the lower housing 370. The displayrests on a center support 382 of the lower housing 370. The pin 364 fitsin a pin slot 384. Although the slot 384 could potentially be a merehole, it is preferred that this be elongated to permit some lateralmovement of the display, which enhances the orientation lockability, tobe described below.

The display 340 rests between a proximal (to the measuring device)support 386 and a distal support 374. The proximal support 386 has acurved raised edge designed to match a curvature of the display 340.Protrusions 390 are provided on a raised edge of the proximal support386 that serve to engage the locking groove 348 of the display 340 whenat least some minimal force provided by a spring 336 and locking slider332 (see also FIG. 12) force the display laterally against the raisededge. This helps to maintain the orientation of the display 340 once ithas been set.

The distal support 374 comprises a spring slot 378 into which the spring336 rests. It also comprises a slider recess 376 into which the lockingslider 332 rests, as well as a corresponding pin slot 380 in which theslider pin 334 rests. The locking slider 332 preferably has a springhole 338 into which a portion of the spring extends. The spring hole 338helps to maintain the spring in position, although this is notessential, and other mechanisms, such as an additional pin, may be used.The slider pin 334 itself is designed to engage one of the locking holes346 of the display. The spring 336 resting in the slot is in a generallycompressed state, such that it provides a force that biases the lockingslider 332 and its slider pin 334 into the display 340.

Thus, a user wishing to orient the display, moves the locking slider 332towards the distal (away from the measuring device) end of the displayassembly 300 and against the spring 336 bias. This causes the slider pin334 to disengage from the locking hole 346 so that the display 340 canbe rotated about is axis about the pin 364. Absent a biasing force, thedisplay 340 is also slightly moved in a distal lateral direction suchthat the protrusion(s) 390 disengage the locking groove(s) 348. Thelower housing 370 also comprises a handle portion 372 that, whencombined with a handle portion 312 of the upper hosing 310, provides aneasy-to-grasp element for the user.

The upper housing 310 may be designed as a three-piece unit or as aone-piece unit. The three-piece configuration comprises a separateproximal support member 320, distal support member 314, and transparentcover 324. In the one-piece unit, these the proximal support member 320,distal support member 314, and transparent cover 324 may be provided asa single unit, either via assembly or construction as a monolithic unit.

The transparent cover 324 (see also FIG. 11), which permits viewing ofthe display screen 350, may comprise legs 326 that rest upon legsupports 318, 322 of the distal support 314 and proximal support 320respectively. Preferably, the legs 326 and leg supports 318, 322 areproportioned such that an upper surface of the transparent cover isflush with upper surfaces of both the distal support 314 and theproximal support 320.

The distal support 314 comprises a slot 316 into which a top portion ofthe locking slider 332 protrudes. A lever 331 may be affixed to a topsurface of the locking slider 332 and serves to form a relatively secureseal of the slider slot 316 such that contaminants cannot readily enterthe slider slot 316. Thus, when the user wishes to reorient the display340, the user moves the lever 331 towards the distal end of the displayassembly 300 and against the spring 336 bias to disengage the display340 from the locking mechanisms (332, 390). Once the display 340 isdisengaged, it may be rotated into a locking position (one in which theslider pin 334 aligns with the locking hole 346 and the locking groove348 aligns with the protrusion 390). The user releases the lever 331 andthe spring 336 biases the locking slider 332 to move the slider pin 334into the locking hole 346 and biases the display 340 against the curvedside surface 388 of the proximal support 386, thereby engaging thelocking groove(s) 348 with the protrusion(s) 390.

Referring to FIG. 13, a pivot arm 391 is provided that permits anadditional axis of rotation for the display assembly 300. The pivot arm391 comprises, at a distal end (away from the measuring device) areceiving slot 392 for a proximal end of the display assembly 300. Theproximal supports 320, 386 can comprise a hole into which a pivot pin398 can be inserted. The pin 398 is supported by a pivot hole 396 in anarm end 394 of the pivot arm 391 formed by a receiving slot 392 intowhich the proximal end of the display assembly 300 is provided. Therotational freedom of the display assembly 300 about the pivot pin 398can be hampered by a frictional fit of the hole of the display assemblyagainst the pivot pin 398. Alternately, or additionally, interactingprotrusions and grooves, or bumps and holes may be provided between thewall edges of the receiving slot 392 and side edges of the proximalsupports 320, 386.

It should be noted that the embodiment shown provides for a rectangularcross section of the support elements of the display assembly 300 andthe pivot arm 391. However any practical cross-sectional shape can beimplemented, such as round, oval, polygonal or other closed curvedshape. Furthermore, an additional pivot arm similar to the pivot arm 391described above could be provided at the end of the pivot arm 391 inorder to permit rotation of the display in three full dimensions.

Furthermore, the rotating mechanisms described above relating to a pinand hole or slot to permit rotation could also be implemented usingsupporting roller, spherical, or other forms of bearings, or could alsobe implemented with a ball socket type arrangement. In the latterarrangement, the locking mechanism could simply be a frictional fit thatmay or may not be adjustable in the frictional forces created. When apivoting mechanism is used, the pivot may be placed central to thedisplay, or offset. Furthermore, the display 340 itself can be locatedat either a proximal or distil end of the display assembly 300 insteadof in a central region.

FIG. 14 illustrates another embodiment of the display. At the distal endof the body 140, a rotatable body section 311 is provided that canrotate about a longitudinal axis B. This section can either be connectedby wires or connected wirelessly to the actual measurement electronics.When connected with wires, stops, e.g., in the way of interferingprotrusions, may be provided the prevent rotation beyond an allowablelimit.

In an embodiment, the display screen 350 is provided directly on therotatable body section 311. In this embodiment, a series of grooves andprotrusions or bumps and holes may be provided on an inner surface ofthe body 140 and outer surface of the rotatable body section 311 inorder to provide discrete orientation positions for this section.Alternately, the rotatable body section 311 can be designed to operatewith a frictional fit so that it can be rotated when a certain force isdeliberately applied but is unlikely to rotate during normal measurementuse.

In a further embodiment, as illustrated in FIG. 14, a display 340similar to that illustrated in FIGS. 8-13 is provided that can berotated about an axis A perpendicular to the longitudinal axis B. Asimilar groove 348 and protrusion (not shown) scheme may be utilized tosecure the orientation, and the slider pin (not shown) operable by alever 331 on a distal support 374 can be provided to engage holes 346 ofthe display 340. In this way, the display screen 350 itself can beprovided with two rotational degrees of freedom, thereby permitting thedisplay position to be optimized during use. It should be noted thatalthough a rigid attachment of the distal support 374 is illustrated inFIG. 14, the attachment could also be implemented in the form of, e.g.,a ball socket, thereby permitting an additional degree of freedom whenorienting the display.

Two final embodiments are illustrated in FIGS. 15A and 15B in which agenerally cylindrical body comprises the extension actuator 237 andgroove 239. In FIG. 15A, the display 340 is generally a flat andrectangular housing on a rotatable body section 311 of the tool body 140that houses the display screen 350 and mounts to the body via a pin 364that is located in a generally central position of the display. Thispermits the display 340 to be rotated for ease of viewing. Asillustrated in FIG. 15B, the pin 364 can be offset from the center. Thisrectangular display 340 can be implemented in the designs shown in allprevious figures.

In all of these designs, it is possible to include an option in whichthe image on display itself can rotate as well, although this would bepractical when the display comprises an array of pixels. FIG. 15Cillustrates such an implementation. As can be seen in FIG. 15C, thecharacters on the display screen 350 are oriented differently dependingon the relative angle of the display screen 350 (and display 340 itself)with respect to the body 311. An angular sensor could be provided todetect the angle of the display relative to the body. If the angle fallswithin, e.g., various 90° quadrants, the image on the display could berotated accordingly by display electronics that sense this angle andadjust the pixels on the display screen 350 accordingly. More complexdesigns could be implemented with, e.g., gravity sensors and the like todetermine a preferred orientation, although this design wouldconsiderably increase costs and would not work as effectively when theplane of rotation is perpendicular to a fixed reference such as agravity vector.

FIG. 15D is a top view of the embodiment shown in FIGS. 15A-15C andillustrates a rotation about the longitudinal axis of a body section 311comprising the display 340, 350, although an embodiment not having thissection 311 rotatable about the longitudinal axis (or rather, havingthis section fixed relative to a front portion) is also possible.

All references, including publications, patent applications, andpatents, cited herein are hereby incorporated by reference to the sameextent as if each reference were individually and specifically indicatedto be incorporated by reference and were set forth in its entiretyherein.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the invention (especially in the context of thefollowing claims) are to be construed to cover both the singular and theplural, unless otherwise indicated herein or clearly contradicted bycontext. Recitation of ranges of values herein are merely intended toserve as a shorthand method of referring individually to each separatevalue falling within the range, unless otherwise indicated herein, andeach separate value is incorporated into the specification as if it wereindividually recited herein. All methods described herein can beperformed in any suitable order unless otherwise indicated herein orotherwise clearly contradicted by context. The use of any and allexamples, or exemplary language (e.g., “such as”) provided herein, isintended merely to better illuminate the invention and does not pose alimitation on the scope of the invention unless otherwise claimed. Nolanguage in the specification should be construed as indicating anynon-claimed element as essential to the practice of the invention.

A variety of embodiments of the invention are described and illustratedherein; variations of those embodiments will become apparent to those ofordinary skill in the art upon reading the foregoing description. Theinventors expect skilled artisans to employ such variations asappropriate, and the inventors intend for the invention to be practicedotherwise than as specifically described herein. Accordingly, thisinvention includes all modifications and equivalents of the subjectmatter recited in the claims appended hereto as permitted by applicablelaw. Moreover, any combination of the above-described elements in allpossible variations thereof is encompassed by the invention unlessotherwise indicated herein or otherwise clearly contradicted by context.It is not the intent of the inventors to surrender or otherwise dedicateany valid claim to the subject matter described herein to the public,and the following claims are intended to capture the entire scope of theinvention herein described.

1. A generally elongated instrument for measuring the depth of a holewith a first edge and a second edge, the instrument having alongitudinal axis, the instrument comprising: a first generallyelongated member substantially oriented along the longitudinal axis andwhich is insertable in the hole, the first member comprising a portionpositionable against a first surface in which the first edge of the holeis formed; a second generally elongated member substantially orientedalong the longitudinal axis and which is slidably connected to the firstmember, the second member comprising a portion positionable against asecond surface in which the second edge of the hole is formed and asensor that generates an electronic signal that varies in relation tothe distance between the first member and the second member; and arotatable electronic display for displaying information representativeof the distance measured by the sensor.
 2. The instrument as claimed inclaim 1, wherein the rotatable electronic display rotates about thelongitudinal axis.
 3. The instrument as claimed in claim 1, wherein therotatable electronic display rotates about a lateral axis that isperpendicular to the longitudinal axis.
 4. The instrument as claimed inclaim 1, wherein the rotatable electronic display rotates about both thelongitudinal axis and the lateral axis.
 5. A depth measurement gage formeasuring a hole depth, comprising: a measurement tool that converts anextension length of a measuring element into a representative electronicsignal; a display assembly connected to the depth measurement gage, thedisplay assembly comprising: a rotatable display that comprises: adisplay screen for displaying a numeric representation corresponding tothe extension length based on the electronic signal received from themeasuring tool; display electronics that receive the electronic signal,converts it into a displayable value, and drives the display to displaythe value; and a locking mechanism that holds the display at aparticular orientation; wherein the rotatable display is rotatable aboutan axis normal to a surface of the display screen; the display assemblyfurther comprising: a housing that connects with and supports therotatable display; the depth measurement gage further comprising: arotation element that allows the rotatable display to rotate about anaxis parallel to a surface of the display screen.
 6. The gage as claimedin claim 5, wherein the rotation element comprises: a pivot arm having aproximal end connected to the measurement tool; and a distal endconnected to the display assembly and having a pivot assembly thatpermits the rotatable display to rotate about the axis parallel to thedisplay screen.
 7. The gage as claimed in claim 5, wherein the rotationelement comprises a cylindrical rotatable body section rotatably mountedto a main body of the gage.
 8. The gage as claimed in claim 5, whereinthe housing comprises upper and lower portions, and the display rests onthe lower portion.
 9. The gage as claimed in claim 5, wherein thelocking mechanism comprises at least one of: a) a pin and hole, and b) agroove and ridge/protrusion element.
 10. The gage as claimed in claim 9,wherein the locking mechanism comprises a biasing spring that forces atleast one of the pin into the hole and the groove into theridge/protrusion.
 11. The gage as claimed in claim 9, wherein thelocking mechanism further comprises a slider with biasing mechanism forengaging and disengaging the locking mechanism.
 12. The gage as claimedin claim 11, wherein the slider comprises a lever affixed to the sliderthat seals a hole that houses a portion of the slider.
 13. The gage asclaimed in claim 5, wherein the rotation element comprises a pin and ahole into which the pin is inserted, the parallel axis defined by alongitudinal axis of the pin.
 14. The gage as claimed in claim 5,wherein the rotation element comprises a ball and socket that furtherallows the rotatable display to rotate about a central point defined bya center of the ball.
 15. A depth measurement gage for measuring a holedepth, comprising: a measurement tool that converts an extension lengthof a measuring element into a representative electronic signal; anelongated housing extending along a longitudinal axis of the measurementtool; a rotatable rectangular display that, when in an initial position,has a side that is parallel to the longitudinal axis, the displaycomprising: a display screen for displaying a numeric representationcorresponding to the extension length based on the electronic signalreceived from the measuring tool; display electronics that receive theelectronic signal, converts it into a displayable value, and drives thedisplay to display the value; and a locking mechanism that holds thedisplay at a particular orientation; wherein the rotatable display isrotatable about an axis normal to a surface of the display screen. 16.The gage as claimed in claim 15, wherein the rotatable display comprisesat least one of a pin and a hole that mates with a respective hole orpin either directly or indirectly attached to the housing.
 17. The gageas claimed in claim 16, wherein the at least one of the pin and hole islocated at a center of the display.
 18. The gage as claimed in claim 16,wherein the at least one of the pin and hold is located near an edge ofthe display.
 19. The gage as claimed in claim 16, further comprisingelectronics for rotating characters relative to the display based on adetected angle of the display to the body or other fixed referenceangle.
 20. A depth measurement gage for measuring a depth of a hole,comprising: a measurement tool that converts an extension length of ameasuring element into a representative electronic signal that iswirelessly transmitted; a display assembly connected to the depthmeasurement gage, the display assembly comprising: a wireless rotatabledisplay that comprises: a display screen for displaying a numericrepresentation corresponding to the extension length based on theelectronic signal received from the measuring tool; a wireless antennaand signal receiver that receives the wirelessly transmitted electronicsignal; and display electronics that receive the electronic signal,converts it into a displayable value, and drives the display to displaythe value; the display assembly further comprising: a housing thatconnects with and supports the rotatable display.
 21. The gage asclaimed in claim 20, further comprising a locking mechanism that holdsthe display at a particular orientation.
 22. The gage as claimed inclaim 20, further comprising: an element permitting rotation of thedisplay about an axis normal to a surface of the display screen; and afurther rotation element that allows the rotatable display to rotateabout an axis parallel to the surface of the display screen.
 23. Agenerally elongated instrument for measuring the depth of a hole with afirst edge and a second edge, the instrument having a longitudinal axis,the instrument comprising: a first generally elongated membersubstantially oriented along the longitudinal axis and which isinsertable in the hole, the first member comprising a portionpositionable against a first surface in which the first edge of the holeis formed; a second generally elongated member substantially orientedalong the longitudinal axis and which is slidably connected to the firstmember, the second member comprising a portion positionable against asecond surface in which the second edge or a base of the hole is formedand a sensor that generates an electronic signal that varies in relationto the distance between the first member and the second member; andaudio electronics that audibly conveys information representative of thedistance measured by the sensor to a user of the instrument.